Variable alternating current coil constructions



March 1, 1960 R. A. RUEHLE 2,927,291

VARIABLE ALTERNATING CURRENT COIL CONSTRUCTIONS Filed April 15, 1957 2 Sheets-Sheet 1 INVENTOR.

46 Robert A. Ruehle @L. BY

' ATTC-FNEY March 1, 1960 R. A. RUEHLE VARIABLE ALTERNATING CURRENT COIL CONSTRUCTIONS 2 Sheets-Sheet 2 Filed April 15, 1957 INVENTOR. Robert A. Ruehle BY ATTORNEY United States Patent VARIABLE ALTERNATIN G CURRENT COIL CONSTRUCTIONS Robert A. Ruehle, Denver, Colo. Application April 15, 1957, Serial No. 652,977 8 Claims. (Cl. 336-149) This invention relates to alternating current devices of the variable type such as auto-transformers, choke coils and the like. Such devices usually employ a wire wound coil with a toroid iron core. A sliding contact is provided which can be adjusted axially of the coil in contact with the individual turns of the coil to vary either the voltage or the usable portion of the winding.

Ideal increments of adjustability require a relatively large number of contacted turns. However, the number of turns in a conventional device are limited by the restricted space available so that less than the ideal number are provided. The reductionin turns requires an increase in the cross section of the iron core and the final result is a heavy unit with relatively coarse increment adjustment.

The principal object of this invention is to provide a' coil with flat foil windings separated by a thin insulating film so that the space lost in round wire windings will be entirely eliminated so that a greatly increased number of turns can be placed in a given space with a resulting increase in increment adjustment and a resulting decrease in core cross section and weight.

Another .object of the invention is to replace the usual longitudinally movable contact slider which is usually placed at the side of the oil with a radially movable slider positioned at the end 'of the coil to still further reduce the space requirements of the unit.

In present devices the contact slider must have sufficient width to overlap at least two turns on the coil and in actual practise, the overlap extends to additional coils. This overlap creates short circuits in the overlapped turns resulting in excessive heating. In present devices, a resistance contact member is provided to reduce the short-circuit in an attempt to reduce heating. Such contact members are short-lived and troublesome.

A further object of this invention is to provide a coil assembly in which the resistance contact member is eliminated by the application of a novel resistance film to the turns of the coil.

Other objects of the invention which result in improved resolution of voltage or inductance, reduction of weight and cost, and increased efficiency will become more apparent from the following description in which reference is had to the accompanying drawings.

In the following detailed description of the invention, reference is had to the accompanying drawing which forms a part hereof. Like numerals refer to like parts in all views of the drawing and throughout the description.

In the drawing:

Fig. 1 is a top view of the improved variable coil device;

Fig. 2 is a side view thereof;

Fig. 3 is a horizontal cross section looking downward on the line 3--3, Fig. 2;

Fig. 4 is a similar cross-section, looking downwardly on the line 44, Fig. 2;

Fig. 5 is a vertical section through the upper portion of the improved coil device, taken on the line 55, Fig. 1; a

Fig. 6 is a detail perspective view illustrating a contact arm employed in the coil device;

Fig. 7 is a perspective view of an alternate coil and core arrangement which may be used in the invention;

Fig. 8 is a top view of the coil of Fig. 7;

Figs. 9 and 10 are circuit diagrams illustrating uses for the improved coil device; and

Fig. 11 is a magnified fragmentary section illustrating a coil construction employed in the improved coil device.

All forms of the improved coil device employ a coil 10 formed from a substantially cylindrical, open-cen-' tered, tight wrapping of metallic foil ribbon, the width of the foil ribbon equaling the total height or length of the coil, and an open-centered, magnetically permeable, core of susbtantially rectangular shape extending through the open center of the coil and about one side thereof. The foil ribbon is covered with an insulating coating, indicated at 40 in Fig. 11, and is preferably formed by wrapping the ribbon tightly on a winding form having a flat side so that the portion of the coil which passes through the open-center of the rectangular core 11 will be flat sided. After the winding is completed, the entire top of the coil is smoothed and polished to expose the edges of the wound foil ribbon.

In the form of the invention illustrated in Figs. 1 and 2, a notch 12 is milled in one side of the top of the coil to receive the upper portion of the core 11. The notch 12 is of sufficient depth to prevent the core 11 from projecting above the top of the coil. The core is supported upon a base plate 13 which is secured to and supported from a transformer base 14. The core 11 may be formed in any desired manner, for instance, it may be formed in two laminated, U-shaped, halves. The U shaped lower portion of the core is inserted upwardly into the coil 10 and the inverted U-shaped upper portion of the core is inserted downwardly in the coil 10 to form the open rectangular outline of the core. The two portions may be strapped together by means of a retaining strap 15 which passes beneath the base plate 13 to rigidly support the core and coil on the transformer base 14.

A relatively thick top block 16 formed of electrical insulating material and corresponding in contour to the base 14 is supported above the coil and core upon suitable frame members 36. The top block 16 is formed with an indented cam cavity 17 in its bottom positioned over the upper surface of the coil 10.

A control shaft 18, axially positioned with reference to the coil 10, extends through a bearing bushing 19 which is locked in the top block 16 between suitable lock nuts 20. A sliding contact arm 21 extends through a diametric slot in the shaft 18 adjacent its lower extremity and projects diametrically therefrom into contact with the inner wall of the cam cavity 17. The contact arm 21 is maintained in place in the shaft 18 by means of a pivot pin 26 passing through an elongated slot 27 in the arm 21. A compression spring 22 surrounding the arm 21 constantly urges the extremity thereof into frictional contact with the wall of the cam cavity 17. A brush holder 24 is mouned on the arm 21 adjacent the outer extremity of the latter and carries a suitable contact brush, such as a carbon brush 25.

The brush 25 is constantly urged downwardly into con: tact with the exposed edges of the foil ribbon by means of a V-shaped leaf spring 23. The leaf spring 23 frictionally bears against the lower surface of a contact plate 37 which is fixedly mounted in the top of the cam cavity 17 and maintains electrical contact therewith.

The contour of the inner wall of the cam cavity 17 is such that when the shaft 18 is rotated to one extreme of its rotative movement, the arm'21 will be urged inwardly toward the shaft 18 so that the brush will be contacting the coil 10 adjacent the inner diameter thereof as indicated at A in Fig. 4 and when turned to the other extreme of its rotative movement, the arm 21 will follow the cam contour to position the brush 25 at the outer circumference of the coil as indicated at B in Fig. 4.

The foil ribbon forming the coil ill is coated with an insulating film prior to winding and is wound tightly to form a solid unit to eliminate the usual air spaces or interstices which cause the Waste space in a wire winding. Since the foil is exceedingly wide, it can be exceedingly thin and still obtain the desired cross section. Therefore the turns in the winding are exceedingly close together and the brush 25 overlaps a plurality of windings. This overlap would ordinarily create a short circuit in the overlapped winds resulting in heat. This is avoided in the improved coil by anodizing the finished upper surface of the coil. The anodizing is applied by an electrochemical process whereby an exceedingly thin film, indicated at 38 in Fig. 11, of aluminum oxide, A1 is formed on the polished edges of the aluminum turns. The electrical resistance of this thin resistance film is sufiiciently high to limit the short circuit current through the brush to a safe value and is sufficiently low so that excessive heat does not result from the flow of the useful current to the brush. The outmost turn of foil terminates in a projecting first contact 28 and the innermost turn of the coil is terminated in a second projecting contact 29. The contact plate 37 is connected to an intermediate contact 39. These contacts can be connected into various electric ciredits to obtain desired voltage and current controls, such as indicated in Figs. 9 and 10. Additional current taps may be brought olf from the coil ill for various usages as will be apparent to those skilled in the art.

In Fig. 7 an alternateform of the coil, designed for more minute control is illustrated. In this form, an iron core 31, corresponding to the core llll previously described, is extended through a hole 32 in the side of and adjacent the upper extremity of a coil 33, similar to the foilwound coil previously described. In the second form, howeventhe core is positioned below the top of the coil so that a brush 34 corresponding to the brush 115 can travel in a continuous spiral around the entire annular area ofithe coil, as indicated by the broken spiral line 39 in Fig. 8. A narrow slot 35 is cut through the coil above the hole 32 to eliminate the large magnetizing current which would be required by the air core above the metallic core 31. The width of the slot is less than the width of the brush 34 so that the latter can travel thcreacross. In this form, a plurality of revolutions of the control shaft would berequired to cause the brush 34 to travel the full radial width of the coil so that a more minute current control can be obtained.

While a specific form of the improvement has been described and illustrated herein, it is to be understood that the saine may be varied within the scope of the appended claims, without departing from the spirit or" the invention.

Having thus described the invention, what is claimed and desired secured by Letters Patent is:

1. A coil for alternating current devices comprising: a ribbon of metallic foil rolled into a relatively tight, hollow coil; an insulating film between the adjacent turns of ribbon in said coil, the edges of the turns of said ribbon being exposed at one extremity of said coil; a contact device movable over. and in contact with the exposed edges of said ribbon; an open-centered, magneticallypermeable core, one side of said core extending through the open center of said coil, the other side of said core extending exteriorly alongside said coil, one end of said core extending through a receiving passage in said coil adjacent the one extremity of said coil.

2. A coil for alternating current devices as described in claim l in which the said one extremity of said coil is provided with asep arating slot formed through the turns 'ofjsaid coil and extending to said receiving passage.

3. Acoil for alternating current devices comprising: a ribbon of metallic foil rolled into a relatively tight,

hollow, cylindrical coil, the width of said ribbon equaling the axial length of said coil; an insulating film between the adjacent turns of ribbon in said coil, the edges of the turns of said ribbon being exposed at one extremity of said coil; an open-centered, magnetic core, one side of said core passing through the open-center of said coil, the end of said core adjacent the exposed edges of said ribbon extending through a receiving-passage in said coil; a top member supported in spaced relation to said exposed edges; an actuating shaft rotatably mounted in said top member in substantially axial relation to said coil; 21 contact arm extending radially from said actuating shaft and being radially movable relative to said shaft; 8. brush member mounted on said contact arm and adapted to contact the exposed edges of the metallic member; resilient means urging said brush member toward the periphery of said coil; and cam means on said top member acting to move said brush member toward the axis of said coil when said actuating shaft is rotated.

4. A coil for alternating current devices comprising: a ribbon of metallic foil rolled into a relatively tight, hollow cylindrical coil; an insulating film between the adjacent turns of ribbon in said coil, the width of said ribbon equaling the axial length of said coil, the edges of the turns of said ribbon being exposed at one extremity of said coil; a contact device movable over and in contact with the exposed edges of said ribbon; and a film of partially conducting material covering the exposed edges of said ribbon and separating the latter from said brush.

5. A coil for alternating current devices as described in claim 4 in which the foil employed is aluminum foil and in which the film of partially conducting material comprises an anodized edge on the turns of ribbon.

6. A coil for alternating current devices as described in claim 5 in which the anodized edge comprises aluminum oxide.

7. A coil for alternating current devices comprising: a ribbon of metallic foil rolled into a relatively tight, hollow, cylindrical coil, the width of said ribbon equ'al ing the axial length of said coil; an insulating film between the adjacent turns of ribbon in said coil, the edges of the turns of said ribbon being exposed at one extremity of said coil; a rectangular, open-centered, laminated, magnetic core, one side of said core passing through the open-center of said coil, the upper end of said core extending through a receiving-passage in said coil; atop member supported above said coil; an actuating shaft rotatably mounted in said top member in substantially axial relation to said coil; 21 contact arm extending radially from said actuating shaft and being radially movable relative to said shaft; a brush member mounted on said contact arm and adapted to contact the exposed edges of the metallic member; a cam cavity formed in said top member about said brush arm; resilient means urging said brush arm against the cam surface of said cam cavity so that said surface will impart a radial movement to said brush arm as said shaft is rotated.

8. A coil for alternating current devices as described in claim 7 having a contact plate in said cam cavity and resilient contact means carried by said brush arm and frictionally contacting said contact plate to carry current between said arm and plate.

References Cited in the file of this patent UNITED STATES PATENTS 926,934 De Forest July 6, 1909 2,716,736 Rex Aug. 30, 1955 2,762,019 Short Sept. 4, 1956 2,799,756 Graham July 16, 1957 OTHER REFERENCES Variac, i955 Bulletin N., 'Cat'alo'g form 424 51 or General Radio 00., January 1931, 1955, page 3. 

